CN108514404B - Optical coherence tomography system - Google Patents
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Abstract
The present invention relates to an optical coherence tomography system. The system comprises a light source, an optical fiber coupler, a reference arm, a sample arm, a signal acquisition module and a signal processing module. The light source provides initial light; the fiber coupler divides the initial light into reference light and sample light; the reference arm transmits the reflected light of the reference light back to the optical fiber coupler; the sample arm detects a sample to be detected by using the sample light, and the sample light generates backward scattering light in the sample to be detected and returns the backward scattering light to the optical fiber coupler; the backward scattered light and the reflected light interfere in the optical fiber coupler to form interference light; the interference light is divided into multi-path interference spectrums by the optical fiber coupler; the signal acquisition module respectively acquires each interference spectrum; and the signal processing module generates a detection image of the sample to be detected according to the spectral line signals of the interference spectra. By the system, virtual image interference and optical signal noise interference can be eliminated, so that the imaging effect of the system is good.
Description
Technical Field
The invention relates to the technical field of optical detection, in particular to an optical coherence tomography system.
Background
Optical Coherence Tomography (OCT) is a non-destructive Optical inspection technique developed in the last 90 years. The OCT is based on an optical signal delay and phase change measuring system of an optical low-coherence interferometer, and backscattering and reflection signals of different depths in a sample are indirectly measured. The OCT generates signals with different contrasts according to different refractive indexes (representing optical scattering characteristics inside the sample) inside the sample, so that the cross section inside the sample can be imaged. The OCT imaging technology has the characteristics of non-radiation, non-contact, high axial direction resolution ratio, no damage, easy endoscopic integration and moderate price on a detected sample, so that the OCT imaging technology is an optical imaging tool with great prospect. At present, the OCT technology has been widely used in the medical diagnosis fields of ophthalmology, skin tissue, angioscopy, orthopedics, and the like. OCT techniques are also increasingly used in industrial applications such as drug coating, material thickness measurement, car paint spraying, etc.
The OCT techniques are classified into time-domain OCT, doppler OCT, frequency-sweep OCT, spectral OCT, and the like according to the difference in indirect delay and phase measurement of sample scattered light. Because the spectral OCT has the advantages that the axial depth scanning is carried out without using a mechanical scanning component, and the axial hierarchical information of the sample can be directly obtained through the Fourier transform of the spectrum, the imaging speed of the system can be greatly improved, and the noise introduced by a mechanical motion scanning structure is avoided. Meanwhile, the absorption of water molecules with the wavelength used by spectral OCT is extremely small, so that the spectral OCT has great success in the fields of ophthalmic medical treatment and diagnosis.
However, conventional spectral OCT is still based on a two-beam interferometric Michelson interferometer (the two arms of the interferometer have a fixed pi phase difference). When the spectral OCT is used for processing interference spectral lines, virtual signals on two sides of a zero optical path difference position are introduced, and therefore virtual image interference exists in imaging of the spectral OCT. In addition, interference of scattered light, reference light, a direct current term, and the like also causes noise of interference spectrum signals to be large. Therefore, the conventional spectral OCT has a large disturbance, resulting in poor imaging results.
Disclosure of Invention
Based on this, it is necessary to provide an optical coherence tomography system for the problem that the interference of the conventional spectral OCT is large, which results in poor imaging results.
An optical coherence tomography system comprising:
a light source providing primary light;
the optical fiber coupler receives the initial light and divides the initial light into a plurality of paths of output light, and the plurality of paths of output light comprise one path of reference light and one path of sample light;
the reference arm is used for receiving the reference light and transmitting the reflected light of the reference light back to the optical fiber coupler;
a sample arm for receiving the sample light; the sample arm detects a sample to be detected by using the sample light, the sample light is scattered at the sample to be detected to generate backward scattered light, and the backward scattered light is transmitted back to the optical fiber coupler; the backward scattering light and the reflected light interfere in the optical fiber coupler to form interference light; the interference light is divided into multiple paths of interference spectrums by the optical fiber coupler, and each path of the multiple paths of interference spectrums is output respectively;
the signal acquisition module is used for respectively acquiring the interference spectrums;
and the signal processing module is used for generating a detection image of the sample to be detected according to the spectral line signals of the interference spectra so as to eliminate the imaging interference of the sample to be detected.
In the optical coherence tomography system, first, the reference light is reflected back to the optical fiber coupler by the reference arm. The sample light forms backscattered light through the sample arm back to the fiber coupler. Second, the fiber coupler receives the backscattered light and the reflected light. The backscattered light and the reflected light interfere with each other in the optical fiber coupler to form interference light. And, the fiber coupler splits the interference light into multiple interference spectra. Then, the signal acquisition module respectively acquires each path of interference spectrum and transmits the spectral line signal of each path of interference spectrum to the signal processing module. And processing the spectral line signals of the interference spectra by the signal processing module, and obtaining the image information of the sample to be detected with depth hierarchy. Because the optical fiber coupler divides the interference light into multiple interference spectrums, the signal processing module carries out image processing according to the interference spectrums, so that virtual image interference and optical signal noise interference can be eliminated, and the imaging effect of the system is better.
In one embodiment, the fiber coupler splits the interference light into three-way interference spectra; the light intensity of any two paths of interference spectra in the three paths of interference spectra is equal, and the phases of the three paths of interference spectra are arranged in an equal phase difference mode.
In one embodiment, the system further comprises a fiber optic circulator; the fiber optic circulator has a first port, a second port, and a third port;
the fiber coupler has three input ends; the three input ends are respectively a first input end, a second input end and a third input end;
wherein the first port is connected to the light source for receiving the primary light; the second port is connected with the first input end, and the second port is used for transmitting the initial light received by the optical fiber circulator to the optical fiber coupler; one path of interference spectrum is transmitted to the signal acquisition module through the first input end, the second port and the third port in sequence; the other path of the interference spectrum is transmitted to the signal acquisition module from the second input end; and the interference spectrum is transmitted to the signal acquisition module from the third input end.
In one embodiment, the system further includes a light path selection module, where the light path selection module selects to receive each path of the interference spectrum at different time, and transmits each path of the interference spectrum to the signal acquisition module respectively.
In one embodiment, the optical path selection module is an electrically controlled optical switch.
In one embodiment, the reference arm comprises a first collimating lens and a mirror, the mirror being perpendicular to an optical axis of the first collimating lens; the first collimating lens converts the reference light into parallel light; the parallel light is incident to the reflector, and the incident angle is 0 degree; the reflecting mirror reflects the parallel light to form the reflected light.
In one embodiment, the distance of the mirror relative to the first collimating lens is adjustable.
In one embodiment, the sample arm comprises a second collimator lens and a detection objective lens, the second collimator lens and the detection objective lens forming a confocal optical path; the second collimating lens converts the sample light into parallel light; the parallel light forms detection light through the detection objective lens and is converged on the sample to be detected, and the backward scattering light formed by scattering of the detection light on the sample to be detected is transmitted back to the optical fiber coupler through the confocal light path.
In one embodiment, the optical axes of the second collimating lens and the detection objective lens are perpendicular;
the sample arm further comprises a scanning galvanometer; the scanning galvanometer is arranged on the optical axes of the second collimating lens and the detection objective lens simultaneously; the parallel light emitted by the second collimating lens is reflected to the detection objective lens by the scanning galvanometer; the incidence angle of the parallel light of the second collimating lens relative to the scanning galvanometer is adjustable.
In one embodiment, the light source is an ultra-wideband light source, and the primary light is low coherence light; the signal acquisition module is a spectrometer.
Drawings
FIG. 1 is a schematic diagram of an optical coherence tomography system according to an embodiment;
fig. 2 is a block diagram illustrating an operation of the signal processing module according to an embodiment.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Fig. 1 is a schematic structural diagram of an optical coherence tomography system 100 according to an embodiment. The optical coherence tomography system 100 includes a light source 110, a fiber coupler 120, a reference arm 130, a sample arm 140, a signal acquisition module 150, and a signal processing module 160. In the present embodiment, the optical signals between the respective devices in the optical coherence tomography system 100 all propagate through the optical fiber.
The light source 110 is used to provide primary light.
The fiber coupler 120 includes a number of inputs and a number of outputs. The fiber coupler 120 receives the primary light through one of the input ends. The fiber coupler 120 splits the primary light into multiple output lights output from the corresponding output terminals. One of the output lights is a reference light, and the other output light is a sample light.
The reference arm 130 receives the reference light and transmits the reflected light of the reference light back to the fiber coupler 120 along the corresponding output end. As shown in fig. 1, the reference arm 130 includes a first collimating lens 131 and a mirror 132. The reflecting mirror 132 is perpendicular to the optical axis of the first collimating lens 131. The first collimating lens 131 converts the reference light into parallel light. The parallel light is incident to the reflecting mirror 132, and the incident angle is 0 °. The mirror 132 reflects the parallel light to form the reflected light. Therefore, the reflected light returns to the fiber coupler 120 along the optical path of the reference light.
The sample arm 140 receives the sample light. The sample arm 140 detects a sample 200 to be measured using the sample light. The sample light is backscattered at the sample to be measured 200, generating backscattered light. The backscattered light is transmitted back to the fiber coupler 120 along an output end corresponding to the sample light. The backscattered light is a scattered wave observed from the direction of the sample light (i.e., the direction of the incident light). As shown in fig. 1, the sample arm 140 includes a second collimator lens 141 and a detection objective lens 142, and the second collimator lens 141 and the detection objective lens 142 constitute a confocal optical path. The confocal optical path refers to an optical path between the second collimating lens 141 and the detection objective lens 142, which is reversible. The confocal light path is used to avoid interference of stray light, and to ensure that the second collimating lens 141 returns the backscattered light signal of the sample. The second collimating lens 141 converts the sample light into parallel light. The parallel light forms probe light via the probe objective 142. The probe light is converged on the sample 200 to be measured. The probe light is scattered on the sample 200 to be measured to form backscattered light. The backscattered light passes through the confocal optical path back to the fiber coupler 120.
The first collimating lens 131 and the second collimating lens 141 are both fiber collimating lenses. The fiber collimating lens is an aspheric lens with fiber pigtail coupling. The fiber collimating lens can collimate the broadband divergent light input by the fiber into free space parallel light and output the free space parallel light. The operating wavelength range of the fiber collimating lens should match the center wavelength and spectral width of the aforementioned broadband light source 110. Further, the chromatic aberration and aberrations of the fiber collimating lens should be as small as possible over the entire operating wavelength range. This ensures that the output light components of different wavelengths are all in the same collimated beam. And simultaneously, different light components of the received parallel reflected light can be returned to the optical fiber with the same coupling efficiency. Furthermore, the fiber collimator lens and the detection objective lens 142 may be convex lenses.
After the backscattered light and the reflected light return to the fiber coupler 120, they interfere with each other in the fiber coupler 120, forming interference light. The interference light is divided into multiple interference spectra by the fiber coupler 120, and each interference spectrum is output from a corresponding input end.
The signal collection module 150 collects each of the interference spectra. The signal acquisition module 150 obtains spectral line signals of each path of interference spectrum.
The signal processing module 160 generates a detection image of the sample 200 to be detected according to the spectral line signals of the interference spectra, so that the interference of the interference spectra on the imaging of the sample 200 to be detected is eliminated.
In the optical coherence tomography system 100, first, the reference light is reflected by the reference arm 130 and returns to the fiber coupler 120. The sample light forms backscattered light through the sample arm 140 back to the fiber coupler 120. Second, the fiber coupler 120 receives the backscattered light and the reflected light. The backscattered light and the reflected light interfere with each other in the fiber coupler 120, and interference light is formed. And, the fiber coupler 120 splits the interference light into multiple interference spectra. Then, the signal collection module 150 collects each path of interference spectrum, and transmits the spectral line signal of each path of interference spectrum to the signal processing module 160. The signal processing module 160 processes the spectral line signals of the interference spectra, and obtains the depth-hierarchical image information of the sample 200 to be measured. Since the fiber coupler 120 divides the interference light into multiple interference spectra, the signal processing module 160 performs image processing according to each interference spectrum, so as to eliminate virtual image interference and optical signal noise interference, thereby making the imaging effect of the above system better.
In this embodiment, the light source 110 is an ultra-wideband light source 110. The primary light is low coherence light. The ultra-wideband light source 110 refers to a light source 110 based on a semiconductor laser or a light emitting diode. The center wavelength of the spectrum of the light source 110 can be selected to be at different positions such as 850nm, 1310nm, 1550nm, etc., according to the sample to be detected. However, the center wavelength of the spectrum of the light source 110 is not limited to this, and different center wavelengths may be selected according to the sample 200 to be measured. For example, the wavelength band of the initial light may be a near infrared wavelength band. Because the near-infrared band transmittance is high, the system has a high imaging effect on the sample 200 to be detected, and high-resolution lossless three-dimensional imaging can be achieved. The ultra-wideband light source 110 is characterized by: the spectral width is large (the full width at half maximum FWHM is more than or equal to 50nm, wherein the FWHM is an abbreviation of full width at half f maximum), and the total output light power can reach more than 20mW (continuous light). The broader the spectral width of the light source 110, the finer the axial resolution of the scattering information detected by the system at different depth locations in the sample. The higher the optical power is, the stronger the scattered light of the sample arm 140 is, the stronger the signal received by the signal acquisition module 150 is, and the better the imaging effect is. Further, the light intensity of the light source 110 should have small fluctuations over the entire spectral width. For example, the light source 110 may be integrated with a fiber collimator. In this manner, light source 110 couples the emitted free-space light into the optical fiber to facilitate subsequent connections.
In this embodiment, the fiber coupler 120 has three input ends and three output ends. The reference light and the sample light are equal in light intensity. The optical fiber coupler 120 divides the interference light into three interference spectra, the light intensity of any two interference spectra is equal, and the phases of the three interference spectra are arranged in equal phase difference. In this system, the splitting ratio of the sample light to the three outputs is 1: 1: 1. the splitting ratio of the interference light to the three input ends is also 1: 1: 1. thus, the phases of the three paths of interference spectrums are arranged in an equal phase difference mode. I.e. the tolerance of the phase of the three-way interference spectrum is
The characteristics of the 3 × 3 fiber coupler 120 ensure that the fixed phase differences of the generated 3 interference lines are:
0，
in this embodiment, the fiber coupler 120 is a 3 × 3 fiber coupler 120. In this way, the signal-to-noise ratio of any path of interference spectrum can be effectively improved, so that the signal amplitude of the sample depth information recovered by the signal processing module 160 is strongest. The 3 x 3 fiber coupler 120 is a six-port fiber optic device. Each port is connected to an external optical circuit via a fiber pigtail. The fiber coupler 120 has a first input c1, a second input c2, a third input c3, a first output c4, a second output c5 and a third output c 6. As shown in fig. 1, the six ports of the 3 × 3 coupler are divided into two groups, i.e., a left group and a right group, and all three ports of the left group in fig. 1 are input ports (i.e., a first input port c1, a second input port c2, and a third input port c3, respectively). The three ports on the right side of fig. 2 are all output ports (i.e., a first output port c4, a second output port c5, and a third output port c 6). Any one of the input ends can be used as an optical input port. Light input from the input terminal can be output through any one of the output terminals. The left and right groups of ports have reciprocity. The operating wavelength range of the coupler should match the center wavelength and spectral width of the broadband light source 110 described above. The additional loss from input to output may be small. The splitting ratio of the fiber coupler 120 remains as uniform as possible throughout the operating wavelength range.
As shown in FIG. 1, the optical coherence tomography system 100 also includes a fiber optic circulator 170. The fiber optic circulator 170 has a first port p1, a second port p2, and a third port p 3. The second port is connected with the first input end optical fiber. The first port receives the primary light. The first port transmits the primary light to the second port. The primary light is transmitted through the second port to an input end of the fiber coupler 120. In this embodiment, the primary light is transmitted from the second port p2 to the first input end c 1. In the three interference spectra, one of the interference spectra is transmitted from the first input end c1 to the signal acquisition module 150 through the second port p 2. The other path of the interference spectrum is transmitted to the signal acquisition module 150 from the second input end c 2. And a path of the interference spectrum is transmitted from the third input end c3 to the signal acquisition module 150.
In the fiber optic circulator 170, the primary light is input through the first port p1 and output through the second port p 2. Light (interference spectrum) input from the second port p2 is output through the third port p 3. And light inputted from the third port p2 is isolated from returning to the first port p 1. This can not only introduce the initial light into the fiber coupler 120, but also extract a certain path of interference spectrum signal and protect the light source 110 from interference spectrum interference.
It should be noted that the second output end c5 of the optical fiber coupler 120 is not used, and the end face light of the second output end c5 can be prevented from being reflected back to the optical fiber coupler 120 by knotting or the like to introduce interference.
In this embodiment, in the reference arm 130, the distance between the reflector 132 and the first collimating lens 131 is adjustable. Specifically, the mirror 132 is a flat mirror, which is mounted on the optical adjustment frame, and reflects the reference light back to the first collimating lens 131 and couples back to the optical fiber again by adjusting the pitch and yaw angles of the mirror 132. Further, in order to avoid saturation and even damage of the signal acquisition module 150 caused by excessive power of the reflected light, the pitch and deflection angles of the mirror 132 can be adjusted away from the optimal reflection angle. A window plate (operating wavelength matched to the center wavelength and spectral width of the light source 110) may also be selected as the mirror 132. The reflected light is formed by specular reflection between the air and the window sheet. Preferably, the mirror 132 and the optical adjustment frame can be fixed on a one-dimensional linear moving platform, and the distance between the mirror 132 and the first collimating lens 131 is changed by adjusting the moving platform, so as to change the optical path length of the optical path of the reference arm 130. Thus, mirror 132 is used to adjust the optical path length difference between the reflected light of reference arm 130 and the scattered light of sample arm 140 to ensure that the optical path length difference is within the interference distance.
As shown in fig. 1, in the sample arm 140, the optical axes of the second collimator lens 141 and the detection objective lens 142 are perpendicular. The sample arm 140 also includes a scanning galvanometer 143. The scanning galvanometer 143 is disposed on the optical axes of the second collimating lens 141 and the detecting objective lens 142. The parallel light emitted from the second collimating lens 141 is reflected by the scanning galvanometer 143 to the detection objective 142. The incident angle of the parallel light of the second collimating lens 141 with respect to the scanning galvanometer 143 is adjustable. Specifically, the scanning galvanometer 143 is a metal-coated flat mirror 132 whose deflection angle can be changed rapidly by current driving. The plane mirror 132 has zero chromatic aberration and aberration. In the system, a scanning galvanometer 143 is mounted in the optical path of the sample arm 140. The normal of the reflection surface of the scanning galvanometer 143 in the initial state forms an angle of 45 degrees with the optical axis of the second collimator lens 141. By quickly changing the included angle between the normal line and the optical axis of the second collimating lens 141, the function of beam scanning is achieved, so that the axial depth light information of the sample 200 to be measured at different transverse positions is obtained. The scanning frequency of the scanning galvanometer 143 is within 100 Hz. Here, the lateral direction refers to a direction in which the sample 200 to be measured is perpendicular to the optical axis of the probe objective 142. The axial direction refers to a direction in which the sample 200 to be measured is parallel to the optical axis of the probe objective 142.
The detection objective 142 focuses the parallel light beams emitted from the second collimating lens 141 and the scanning galvanometer 143 onto the surface of the sample to be detected. Since the wavelength range of the input light is wide, the configuration of the achromatic lens group needs to be selected. The operating wavelength range of the detection objective 142 should match the center wavelength and spectral width of the light source 110. The focal length of the detection objective 142 should be small and the aperture should be large, so that the scattered light of the detection sample can be received as much as possible. Meanwhile, the light spot size of the convergent point can be reduced due to the larger caliber, and the detection of the transverse resolution of the high sample to be detected 200 can be realized. In the present system, since the second collimating lens 141 and the detecting objective lens 142 form a confocal optical path, the detecting sample needs to be strictly placed at the focal plane position of the detecting objective lens 142, so that the detection is accurate.
The optical coherence tomography system 100 also includes an optical path selection module 180. The optical path selection module 180 selects to receive the interference spectra at different times, and transmits the interference spectra to the signal acquisition module 150. The optical path selection module 180 plays a role of gating the interference spectrum between the fiber coupler 120 and the signal acquisition module 150. Thus, interference of each path of interference spectrum can be avoided.
The light path selection module 180 is an electrically controlled optical switch. The electric control optical switch is an optical path on-off selection module triggered and controlled by an electric signal. The wavelength range of operation of the electrically controlled optical switch should match the center wavelength and spectral width of the broadband light source 110 described above. The on-off switching response time of the electric control optical switch can be less than 1ns, and the working wavelength range can reach more than 100 nm. Therefore, the electric control optical switch is suitable for the system to switch the channel signals at high speed. Therefore, the number of the signal acquisition modules 150 can be saved in a time-division selective receiving mode, and the cost is saved. Specifically, the electrically controlled optical switch has a fiber pigtail for connecting to the fiber coupler 120 and the fiber circulator.
The signal acquisition module 150 is a spectrometer. Further, the spectrometer may employ a fast spectrometer. A fast spectrometer is a device that detects the relative power intensities of different wavelength components of an input optical signal. The range of wavelengths to which it can respond should match the center wavelength and spectral width of the light source 110. In particular, the spectrometer may be an architecture based on a high-speed line-array cmos (complementary Metal Oxide semiconductor) camera. Namely, the input light is converted into free space parallel light to be emitted through a collimating lens (a beam expander is required to be added in partial cases). The free space parallel light emergent has a certain light spot size. The parallel light is incident on a diffraction grating (which may be a reflective or transmissive grating). The parallel light is separated by the grating through different diffraction angles according to Bragg diffraction. The incident angle of the parallel light is selected to maximize the diffraction efficiency of the grating. The emergent diffracted light is converged on a receiving surface of the linear CMOS camera through an achromatic focusing lens. Each receiving pixel of the CMOS camera (which may be a photosensitive material such as Si, AlGaAs or InGaAs depending on the operating wavelength) corresponds to a certain wavelength component of the incident light of the fast spectrometer. And obtaining the spectral information of the incident light according to the photosensitive intensity of each pixel. In particular, the fast spectrometer is provided with a fiber coupling interface. The spectrum acquisition rate of the fast spectrometer can reach 100k spectral lines/second. The spectrometer has a high-speed data readout interface and a large-capacity cache, so that a large amount of spectral line data collected at high speed is provided to the signal processing module 160 for data processing in real time. By applying the rapid spectrometer, spectral line data of each path of interference spectrum can be accurately obtained.
The fast spectrometer obtains three paths of interference spectra through the electrically controlled optical switch. The light intensities of the three interference spectra are respectively marked as I1(k)，I2(k)，I3(k) (corresponding to the first input c1, the second input c2, and the third input c3, respectively, of the fiber coupler 120). From the characteristics of the 3 × 3 fiber coupler 120, assume that I1(k) Has an intrinsic phase of
I2(k) Has an intrinsic phase of 0, I3(k) Has an intrinsic phase of
Fig. 2 is a block diagram illustrating the operation of the signal processing module 160 according to an embodiment. The signal processing module 160 receives the three-way fast spectrometer spectral lines. The signal processing module 160 recovers the image by applying the three-phase algorithm. Firstly, eliminating a virtual image, and then eliminating a direct current term and an interference noise term through coefficient operation, thereby obtaining scattering signal amplitude values a (z) at different depths in the sample. Each processed spectral line corresponds to axial information at a certain position, i.e. a so-called a-Scan spectral line. And then the axial depth information images of the object to be measured at different transverse positions are formed through synchronization with the scanning galvanometer 143. This forms a cross-sectional scatter amplitude image of the sample 200 to be measured, the so-called B-Scan image. The equal three-phase algorithm of the system is as follows:
firstly, according to a data processing method of a traditional SD-OCT system, spectral lines S of 3 interference spectra acquired by a fast spectrometer are processedi(lambda) conversion from the wavelength domain to the wavenumber domain Si(k) In that respect The transformation method comprises the following steps: k 2 pi/λ ( i 1, 2, 3, is the identity of each line; Si(k) And 3X 3 optical fiber coupler120, the first input terminal c1, the second input terminal c2, and the third input terminal c3) in a one-to-one correspondence. Will Si(k) Carrying out spline interpolation of wave number domain to obtain spectral line signal I of wave number domain uniform samplingi(k) According to the SD-OCT properties, there are:
in the formula (1), ERIs the intensity of the reference light, a (z) the backscattering information of the internal hierarchy of the sample 200 to be measured, k is the independent variable of wave number, n is the refractive index of the sample,
i.e. the corresponding phase components of the three spectral lines (in turn
0，
) And i is an imaginary unit.
Next, as shown in FIG. 2, for Ii(k) And executing the following three-phase algorithm operations:
Hi(z)＝FT[Ii(k)]，(i＝1，2，3) (2)
in the formula (2), FT represents a fourier transform.
By the operations of the equations (3) and (4), the virtual image of the sample 200 to be measured can be eliminated.
Direct-current term interference and noise interference of the three-way interference spectrum can be eliminated through the formula (5).
From the above operation, an optimized spectral line h (z) for eliminating the dc term, the virtual image and the noise interference can be obtained from the three interference spectra. The internal hierarchical backscattering information a (z) of the sample is proportional to H (z), the A-Scan line. The A-Scan spectral lines at different positions on the surface of the sample in the transverse direction can be obtained by the back-and-forth movement of the scanning galvanometer 143, and finally, all the A-Scan spectral lines are combined to obtain a cross-section B-Scan image of the sample.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (8)
1. An optical coherence tomography system, comprising:
a light source providing primary light; the optical fiber coupler receives the initial light and divides the initial light into a plurality of paths of output light, and the plurality of paths of output light comprise one path of reference light and one path of sample light;
the reference arm is used for receiving the reference light and transmitting the reflected light of the reference light back to the optical fiber coupler;
a sample arm for receiving the sample light; the sample arm detects a sample to be detected by using the sample light, the sample light is scattered at the sample to be detected to generate backward scattered light, and the backward scattered light is transmitted back to the optical fiber coupler; the backward scattering light and the reflected light interfere in the optical fiber coupler to form interference light; the interference light is divided into multiple paths of interference spectrums by the optical fiber coupler, and each path of the multiple paths of interference spectrums is output respectively; the optical fiber coupler divides the interference light into three paths of interference spectrums; the light intensity of any two paths of interference spectra in the three paths of interference spectra is equal, and the phases of the three paths of interference spectra are arranged in an equal phase difference manner;
the signal acquisition module is used for respectively acquiring the interference spectrums;
the signal processing module is used for generating a detection image of the sample to be detected according to each path of spectral line signal of the interference spectrum so as to eliminate imaging interference of the sample to be detected;
the system further includes a fiber optic circulator; the fiber optic circulator has a first port, a second port, and a third port;
the fiber coupler has three input ends; the three input ends are respectively a first input end, a second input end and a third input end;
wherein the first port is connected to the light source for receiving the primary light; the second port is connected with the first input end, and the second port is used for transmitting the initial light received by the optical fiber circulator to the optical fiber coupler; one path of interference spectrum is transmitted to the signal acquisition module through the first input end, the second port and the third port in sequence; the other path of the interference spectrum is transmitted to the signal acquisition module from the second input end; and the interference spectrum is transmitted to the signal acquisition module from the third input end.
2. The system according to claim 1, further comprising a light path selection module, wherein the light path selection module selects to receive each path of the interference spectrum at different time and transmit each path of the interference spectrum to the signal acquisition module respectively.
3. The system of claim 2, wherein the optical path selection module is an electrically controlled optical switch.
4. The system of claim 1, wherein the reference arm comprises a first collimating lens and a mirror, the mirror being perpendicular to an optical axis of the first collimating lens; the first collimating lens converts the reference light into parallel light; the parallel light is incident to the reflector, and the incident angle is 0 degree; the reflecting mirror reflects the parallel light to form the reflected light.
5. The system of claim 4, wherein a distance of the mirror relative to the first collimating lens is adjustable.
6. The system of claim 1, wherein the sample arm comprises a second collimating lens and a detection objective, the second collimating lens and the detection objective constituting a confocal optical path; the second collimating lens converts the sample light into parallel light; the parallel light forms detection light through the detection objective lens and is converged on the sample to be detected, and the backward scattering light formed by scattering of the detection light on the sample to be detected is transmitted back to the optical fiber coupler through the confocal light path.
7. The system of claim 6, wherein the optical axes of the second collimating lens and the detection objective are perpendicular;
the sample arm further comprises a scanning galvanometer; the scanning galvanometer is arranged on the optical axes of the second collimating lens and the detection objective lens simultaneously; the parallel light emitted by the second collimating lens is reflected to the detection objective lens by the scanning galvanometer; the incidence angle of the parallel light of the second collimating lens relative to the scanning galvanometer is adjustable.
8. The system of claim 1, wherein the light source is an ultra-wideband light source, the primary light is low coherence light; the signal acquisition module is a spectrometer.
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